A booster refers to a device that boosts pedal force by a driver which is transmitted from a brake pedal to a master cylinder. An electric booster refers to a device that interprets pedal force by a driver as an electrical signal and drives a motor based on the interpreted electrical signal, thereby producing braking pressure by pressing the master cylinder. As electric vehicles and hybrid vehicles universally come into use, recently, the electric booster attracts the attention as a device that is substituted for a hydraulic booster.
A process of producing braking pressure using the electric booster will be briefly introduced with reference to FIG. 1.
FIG. 1 is a view illustrating a braking system including a typical electric booster.
Referring to FIG. 1, when a driver steps on a pedal 1, pedal force of the driver is transmitted to a sub master cylinder 2. A solenoid valve 3, which is connected to the sub master cylinder 2, forms a hydraulic line P1 from the sub master cylinder 2 to a pedal simulator 4. The pedal simulator 4 provides reaction force to the pedal 1 so as to allow the driver to feel the pedal force. An oil reservoir 9 is connected to a master cylinder 8.
Meanwhile, a stroke sensor 5 is mounted to the pedal 1 so as to sense a stroke using a rotation angle of the pedal 1. An ECU 6 recognizes required braking force of the driver based on the sensed stroke, drives a motor 7 based on the braking force, and moves a piston 10 forward in conjunction with the motor 7, thereby producing braking pressure by pressing the master cylinder 8. In this case, the ECU 6 properly feedback controls the braking pressure using pressure sensors 11 which are installed in the sub master cylinder 2 and the master cylinder 8.
In the case of the electric booster, highly reliable operations of the motor and the solenoid valve are very important factors. In a case in which the solenoid valve is not normally operated due to mechanical and electrical defects, a fatal problem about braking safety may occur.